This invention relates in general to bearings for supporting shafts for rotation. In particular, this invention relates to an improved structure for a center bearing assembly having an adjustable pneumatic support member.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joints provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
In some vehicles, the distance separating the engine/transmission assembly and the axle assembly is relatively short. For these vehicles, the driveshaft assembly can be formed from a single, relatively long driveshaft tube having the first and second end fittings secured to the ends thereof. In other vehicles, however, the distance separating the engine/transmission assembly and the axle assembly is relatively long, making the use of a single driveshaft tube impractical. For these vehicles, the driveshaft assembly can be formed from a plurality of (typically two) separate, relatively short driveshaft sections. In a compound driveshaft assembly such as this, a first end of the first driveshaft section is connected to the output shaft of the engine/transmission assembly by a first universal joint, a second end of the first driveshaft section is connected to a first end of the second driveshaft section by a second universal joint, and a second end of the second driveshaft section is connected to the input shaft of the axle assembly by a third universal joint.
A compound driveshaft assembly that is composed of two or more separate driveshaft sections usually requires the use of a structure for supporting the intermediate portions thereof for rotation during use. A typical intermediate support structure for a driveshaft assembly (which is commonly referred to as a center bearing assembly) includes an annular bearing having an inner race that engages one of the driveshaft sections and an outer race that supports the inner race for rotation relative thereto. The outer race of the annular bearing is supported within a generally annular support member that is usually formed from a relatively resilient material, such as rubber. The resilient support member is, in turn, supported within a rigid bracket that is secured to a support surface provided on the vehicle. Thus, the center bearing assembly functions to support the intermediate portion of the driveshaft assembly for rotation during use. Many center bearing assembly structures of this general type are known in the art.
The resilient support member is provided in the center bearing assembly to absorb vibrations of the driveshaft assembly and thus minimize the magnitude of such vibrations that are transmitted therethrough to the vehicle frame. However, when such vibrations of the driveshaft assembly occur at frequencies that are at or near the natural resonant frequency of the resilient support member in the center bearing assembly, then the center bearing assembly may not absorb such driveshaft assembly vibrations as effectively as desired. To prevent this from occurring, it is known to provide a resilient support member in the center bearing assembly having a natural resonant frequency that is different from the frequencies of the vibrations that are generated by the driveshaft assembly under normal operating conditions of the vehicle. However, it has been found that the range of the frequencies of the vibrations that are generated by the driveshaft assembly can vary, not only from type of vehicle to another, but also under varying operating conditions of the same vehicle. Thus, it would be desirable to provide a center bearing assembly having a natural resonant frequency that can be adjusted in accordance with the operating conditions of the vehicle.